The present invention relates to a method of composite casting of a one-piece cast tool which comprises at least a first portion which comprises the working component of the tool and which is manufactured from steel, and a second portion which comprises the body component of the tool and which consists of or comprises grey iron, there being formed an interconnection zone between the steel and the grey iron.
In the production of tools for sheet metal working, for example cutting, hole making, bending or other shaping, previous practice has generally been to separately produce a tool body by casting of grey iron. The cast tool body has often required heat treatment and thereafter machining in order to create the requisite seats, holes for guide stub shafts, bolt holes etc., so that securing is made possible of working components, for example steel cutters, for carrying out the working operations proper for which the tool is intended. These working components have been manufactured from steel and the point of departure has often been bar material, the working components having been machined to the correct configuration, provided with apertures for guide stub shafts, fixing bolts and the like. This has been often followed by heat treatment, whereafter additional machining, for example grinding, has been carried out.
To produce a tool in the above-outlined manner is extremely time-consuming and expensive, and is often therefore determinative of the time consumption that is required for the new production of different sheet metal products.
WO 03/041895 discloses a one-piece cast composite tool which consists of two different material qualities, as well as a method of manufacturing such a tool.
According to the prior art technology, two different material qualities are cast in one and the same mould, steel being cast for forming working components in the tool, while grey iron has been cast for producing the tool body proper. Between the two material qualities, an interconnection zone is formed where, to some degree, mixing of the two material qualities may take place. The prior art technology suffers from numerous problems since it does not offer any possibility of positioning the interconnection zone in the tool in such a manner that the mechanical strength of the interconnection zone can be optimised.
In order for the interconnection zone to achieve the requisite quality, careful and accurate control is required of the temperature of the material which is cast first, before casting can take place of the material which is cast last. The prior art technology offers no such possibilities.
Finally, the prior art technology otters no possibility of orienting, in a suitable manner, the interconnection zone in a mould for producing the tool.
It is desirable to design the method intimated by way of introduction so that it obviates the drawbacks inherent in the prior art technology. In particular, it is desirable to design the method according to the invention so that the position of the interconnection zone may be optimised in view of mechanical strength aspects. It is also desirable to design the method according to the invention so that a superior control of the temperature conditions in and at the interconnection zone is created on casting of the last cast material. It is also desirable to design the method according to the invention in such a manner that the orientation of the interconnection zone in a mould may readily be controlled.
According to an aspect of the present invention, a method is characterised in that the casting process is carried out in a single mould which is kept unchanged and closed throughout the entire casting process, that the steel is cast first and in a direction from beneath and upwards, that after the casting of the steel a pause is made, and that the casting of the grey iron is carried out only when the temperature of the steel in the intended interconnection zone has fallen to a first temperature corresponding to the liquidus temperature of the steel minus approx. 30° to 150° C.